Building automation systems are a common feature in many commercial buildings and are becoming more common in residential buildings. Generally speaking, a building automation system or “BAS” includes computer hardware and software that monitors and controls various possible mechanical and electrical systems in a building. For example, the BAS may involve a computer system in communication with heating and lighting control systems. Occupancy sensing through either ultrasonic or infrared based sensors is a common feature of many BAS. With occupancy sensing, a BAS is able to provide lighting control and climate control taking into account the presence or absence of occupants.
Conventional BAS systems using ultrasonic or infrared occupancy sensing, however, suffer from some drawbacks. Conventional occupancy sensing systems often suffer from false positives—falsely identifying an occupant in a space or falsely indicating a space is empty. For example, conventional occupant systems can lose track of an occupant in a space when an occupant is within a space but is still, such as when someone is sitting still at their desk. Similarly, a blowing curtain can falsely be detected as the presence of an occupant in a space. False positives often result in inefficient building control and can cause occupants to temporarily or permanently disable the sensor.
Sensor manufacturers and BAS engineers have ameliorated some of the shortcomings in conventional occupancy sensing systems through sensitivity adjustments, e.g., more or less motion over more or less a period of time required to trigger a sensor, and motion time-outs, e.g., if no motion is detected for a period of time then assume no occupant, as well as complex advanced signal processing, fuzzy logic, and probabilistic models. While some of these improvements to conventional occupant sensors may prove beneficial, shortcomings in such systems persist.
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